1. Field of the Invention
The present invention is directed to a cathode ray tube apparatus of the liquid cooling type which is particularly suitable for use with video projectors and the like.
2. Description of the Prior Art
Typical color video projectors include three cathode ray tubes which supply the red, green and blue color signals to produce the corresponding colors on the projection screen. The picture images from the cathode ray tubes are magnified and then projected onto a screen by a lens system. Cathode ray tubes used for this type of application must have a higher brightness as compared with conventional cathode ray tubes. Consequently, the tubes are driven by relatively high voltage with high current densities. This increased drive causes an increased emission of X-rays and also leads to deterioration of the phosphor surfaces because of the rise in temperature on the phosphor screens.
There have been some attempts to avoid the X-rays radiated from the cathode ray tubes by employing a glass having a large X-ray absorption coefficient. However, such glass is likely to cause a browning phenomemon caused by the impingement of the electron beam, resulting in a decrease of brightness. Consequently, it has become practice to use a glass whose X-ray absorption coefficient is relatively small to avoid such browning, and increase the thickness. However, if the thickness of the phosphor panel is increased the heat radiation effects from the panel are lowered and a deterioration of brightness caused by a rise in temperature of the phosphor screen is made more of a problem.
In order to improve the deterioration of brightness caused by the rise of temperature on the phospor screen, a cathode ray tube apparatus of liquid-cooling type has been proposed in an application filed on behalf of the same assignee as the present application, and appearing in U.S. Ser. No. 156,204.